package com.demo.sort;

import java.util.Arrays;

public class MergeSort {


    public static void main(String[] args) {
        int[] arr  = {4,8,7,5,6,9,3,2,1};
        sort(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void sort(int[] arr){
        int[] temp=new int[arr.length];
        sort(arr,0,arr.length-1,temp);
    }

    private static void sort(int[] arr,int left,int right,int[] temp){
        if(left<right){
            int mid = (left+right)/2;
            sort(arr,left,mid,temp);
            sort(arr,mid+1,right,temp);
            merge(arr,left,mid,right,temp);
        }
    }

    private static void merge(int[] arr,int left,int mid,int right,int[] temp){
        int i=left;
        int j=mid+1;
        int t=0;
        while (j<=mid && j<=right){
            if(arr[i]<arr[j]){
                temp[t++]=arr[i++];
            }else{
                temp[t++]=arr[j++];
            }
        }
        //左边的元素
        while (i<=mid){
            temp[t++]=arr[i++];
        }
        while (j<=right){
            temp[t++]=arr[j++];
        }
        t=0;
        while (left<=right){
            arr[left++]=temp[t++];
        }
    }


}
